| Organic-inorganic composite materials are important materials for the flexible energy storage capacitor.With the increased demands for electronic devices,it is necessary to synthesize flexible energy storage capacitors with high dielectric constant,low dielectric loss and high energy storage density.In this paper,Ba0.4Sr0.6Ti O3?BST?/PVDF composite film was prepared by a conventional solution blending method using BST powder synthesized by a sol-gel method as inorganic fillers and polyvinylidene fluoride?PVDF?as the organic matrix.The effects of doping and coating modification based on BST powders on the properties of composite films were systematically investigated.We discussed the properties of Y/Mn-doped BST/PVDF,Y/Mn-dopedBST@Zr O2/PVDF,Y-BST@Mn-BST/PVDFand Y-BST@Mn-BST@Zr O2/PVDF composite films in detail.Main tasks are as follows:Firstly,BST powders were synthesized by the sol-gel method and the BST filler contents in BST/PVDF composite film were optimized.With the ratio of water to acid of 1:1.1,annealing temperature of 800?,PVP/Ti ratio value of 3:400 in sol and milling time of 32 hours,the uniform small dispersed BST particles with no impurity were prepared.BST/PVDF composite films were prepared by mixing the refined BST powders and PVDF by the conventional solution blending method.The influences of 0?40%BST filler content on the properties of BST/PVDF composite film were investigated.The results show that with the increase of BST fillers,the dielectric constant and the dielectric loss of BST/PVDF composite film gradually increase.At the electric field of 600k V/cm,BST/PVDF composite film with20%BST filler contents has better comprehensive performances with the energy storage density of 4.328J?cm-3.Secondly,we investigated the dielectric and energy storage properties of Y/Mn-doped BST/PVDF?YMx/PVDF?composite film and Y/Mn-doped BST/PVDF?YMx@Zr O2/PVDF?composite film with 1?4%Mn concentrations.With increasing Mn concentration,the dielectric constant of YMx/PVDF composite film increases first and then decreases,and the dielectric loss decreases first and then increases.At 1k Hz,YM3/PVDF composite film has the dielectric constant of 20.9 and the minimum dielectric loss of 0.042.The energy storage density of YM3/PVDF composite film is 4.885J?cm-3,which is 1.13 times of that of BST/PVDF composite film at 600k V/cm,describing the donor-acceptor codoping can increase the energy storage density of composite films.On this foundation,the properties of YMx@Zr O2/PVDF composite films were investigated.YM3@Zr O2/PVDF composite film exhibits the better comprehensive performances with a maximum dielectric constant of 18.4and a minimum dielectric loss of 0.020 at 1k Hz.The energy storage density of YM3@Zr O2/PVDF composite film is 5.670J?cm-3,which is 1.13 times of that of BST/PVDF composite film at 600k V/cm.These experimental results illustrate that coating Zr O2on the surface of BST fillers can reduce the dielectric loss of the composite film and increase the energy storage density.Thirdly,we investigated the dielectric and energy storage properties of Y-BST@Mn-BST/PVDF?Y@Mx/PVDF?compositefilmand Y-BST@Mn-BST@Zr O2/PVDF?Y@Mx@Zr O2/PVDF?composite film with 0?5%Mn concentrations in shell layer.With increasing Mn concentration,the dielectric constant of Y@Mx/PVDF composite film first increases and then decreases,and the dielectric loss changes slightly.At 1k Hz,Y@M3/PVDF composite film exhibits a maximum dielectric constant of 16.5 and a lower dielectric loss of 0.027.The energy storage density of Y@M3/PVDF composite film is 6.287J?cm-3,which is 1.45 times of that of BST/PVDF composite film at 600k V/cm.This result evidences that the core-shell structure formation of the BST powder with dopant and acceptor can increase the directivity of space charge under the electric field and realize the separation of positive and negative charges to increase the energy storage density of the composite film.Further,the properties of Y@Mx@Zr O2/PVDF composite film were studied.The optimized sample Y@M3/@Zr O2/PVDF has the maximum dielectric constant of 20.9 and the minimum dielectric loss of 0.024.The energy storage density of Y@M3/@Zr O2/PVDF composite film is 7.555J?cm-3,which reaches 1.75 times of that of BST/PVDF composite film when the electric field is 600k V/cm.This result further proved the zirconia coating on the BST fillers with core-shell structure can increase the dielectric constant,decrease dielectric loss,and evidently improve the energy storage density of the BST/PVDF composite film. |
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